Astrobiology

What is big history? This emergent and interdisciplinary field, enriched and pioneered by Dr. David Christian of Macquarie University, encourages a more holistic understanding of human events than does the traditional study of history. While historians are concerned with understanding the past in context, and considering cause and effect in human terms, big historians are concerned with understanding the past not only in its immediate human historical setting, but in the context of scientific and physical laws of nature as well. If history is written by the victor, then big history is written in the stars themselves.

Dr. Christian, bolstered by the support of philanthropist Bill Gates, first injected big history into the public sector with a 2011 TED Talk, providing an 18 minute overview of world history. In this sensational talk, which has garnered more than 5 million views since its publication, Dr. Christian identifies the basic principles of big history, including the concept of Goldilocks conditions and the various “thresholds” of complexity that we observe in the universe. At various moments in the cosmic past, Christian states, certain Goldilocks conditions have come about, in which “not too little, and not too much” of certain components — usually energy or mass — have allowed the universe to reach states of increasing complexity.

Starting at the Big Bang and the first moment of time itself, Christian traces the cause-and-effect of each moment and identifies these thresholds. He highlights the six universal thresholds of complexity as follows:

In the last part of my philosophy series, “Thinking about the ‘Metaphysics’ in Metaphysical Naturalism,” I discussed cosmology and the origins of our universe from a naturalist and atheistic perspective. In this next part of the series I will be focusing more particularly on the origin of life in our universe (at least on the only planet currently known to host life, i.e. Earth), and the evolution of lifeforms from simple states to the intelligent minds of human beings today. This journey will require discussing: 1) the abiogenesis of life from non-living matter, 2) the evolution of biological diversity from common descent, 3) and the mind-body physicalism of human minds in a naturalist universe.

The planet Earth has been around for about 4.6 billion years, when a cloud of interstellar gas — filled with particles of ice, dust, rock, and other particles — collapsed to a point of concentrated mass, causing rising heat and the formation of our Sun. Most of the matter in this collapsing nebula fell into our Sun, but other material formed into a planetary disc in orbit around the Sun, causing particles to collide and eventually planets to take shape from cumulative bombardments with solid objects. The third planet from our Sun, Earth, happened to be in the Habitable Zone, which is the region in a solar system where a planet is neither too close nor too far from its star to form liquid water. Earth eventually formed liquid oceans on its surface and also an atmosphere with just the right greenhouse balance for the planet to be neither too hot nor too cold for complex life. The first surviving fossils of life date to about 3.5 billion years ago (about a billion years into our planet’s history) and scientists estimate that life on Earth could have began anywhere from 3.9-3.5 billion years ago.

This sequence of events has left us with a vexing question: what started life on Earth so long ago and how did it get to the point of us humans beings here today?